- LAST REVIEWED: 10 May 2017
- LAST MODIFIED: 11 January 2018
- DOI: 10.1093/obo/9780199363445-0006
- LAST REVIEWED: 10 May 2017
- LAST MODIFIED: 11 January 2018
- DOI: 10.1093/obo/9780199363445-0006
The first modern oil wells were constructed in the middle of the 19th century. Over geological time oil and gas in conventional reservoirs, mainly permeable sandstones and limestones, have accumulated in structural or stratigraphic traps formed by impermeable caprock. Unconventional resources are those that have not accumulated in traps but remain broadly disseminated throughout host rocks—typically siltstones, mudstones, tight sands, or shales with low permeability. The flow of oil and gas to wells can be stimulated by injecting fluids under high pressures into wells to fracture the reservoir rock hydraulically. Since the first commercial application in 1949, millions of wells have been hydraulically fractured throughout the world. The combination of horizontal drilling with hydraulic fracturing in the 1990s resulted in a production technology that is economical for developing unconventional hydrocarbons. In directional drilling, a vertical borehole is constructed to the depth of the unconventional deposit and then the direction is changed and an extended hole is drilled along the axis of the deposit leading to a long connection of the borehole with the hydrocarbon bearing unit that can be hydraulically fractured. Hydraulic fracturing has become a contentious topic for the oil industry, for government regulators, for environmental groups, and for the public. Several issues form the bones of contention. The potential impact of the development of unconventional hydrocarbons on regional water resources is an issue. Some chemical additives in the fracturing fluid are toxins, and concerns about contamination of drinking water aquifers have been raised. Some of the injected fracturing fluids come back out of the well when production starts (flowback water), and brines associated with the reservoir rocks also are produced along with the hydrocarbons (produced water). Contamination of groundwater, surface water, and soils with these fluids must be avoided. One method for disposing of contaminated flowback and produced water is by injection into deep wells. Injection of substantial quantities of fluids into the subsurface can cause earthquakes and induced seismicity is a concern. The production of hydrocarbons is not 100 percent efficient. Leakages during production are cause for alarm because methane is a powerful greenhouse gas that enhances climate warming. The construction of well pads, roads, and pipelines can impact ecosystems by habitat fragmentation and erosion. Other issues that can be important to communities in areas where hydrocarbons are being produced include air quality, noise and light pollution, boom-bust economic cycles, and changes in social structure.
Impact on Water Quantity
Development of oil and gas wells in tight formations requires water for drilling and for hydraulic fracturing. Much of the needed water to date has been taken from local freshwater sources, either surface water or groundwater. Kondash and Vengosh 2015 reports that the mean volume of water used for all shale gas production between 2012 and 2014 in the United States is 116 million m3 per year. Chen and Carter 2016 analyzes data at the individual well level between 2008 and 2014 and finds a wide range of water usage—1,000 to 30,000 m3 of water is required to produce shale gas. This varied range is likely influenced by geology, length of horizontal laterals, and number of stages. Regardless of location, water usage rates for most states increased during the six-year period. This amount of water is relatively small in comparison to amounts for other uses; for example, Murray 2013 indicates that the total annual water use by oil and gas companies in Oklahoma in 2011 represented less than 1 percent of all water used. Nevertheless, in water-stressed areas or in more humid areas during times of drought or low flow of headwater streams, Nicot and Scanlon 2012 argues, water used for hydraulic fracturing may have to be restricted. Also, although water use for development of unconventional hydrocarbon resources is a fraction of water use in urban areas, Fry, et al. 2012 suggests that public perceptions may lead to political conflicts. Judged in comparison with other use of water for energy resources (e.g., for thermoelectric power generation), the analyses of Grubert, et al. 2012 indicate that total water use may decline from use of natural gas from unconventional resources for thermoelectric power generation.
Chen, H., and K. E. Carter. 2016. Water usage for natural gas production through hydraulic fracturing in the United States from 2008 to 2014. Journal of Environmental Management 170:152–159.
Uses publicly available data (FracFocus) and other published studies to provide insight into the relationship between water usage and shale gas production. These insights are focused on fourteen continental states and show trends in temporal nature, composition (e.g., fresh versus recycled), and location.
Fry, M., D. J. Hoeinghaus, A. G. Ponette-González, R. Thompson, and T. W. La Point. 2012. Fracking vs. faucets: Balancing energy needs and water sustainability at urban frontiers. Environmental Science & Technology 46.14: 7444–7445.
Summary of water use for hydraulic fracturing relative to urban water use. The public in the Dallas–Fort Worth area has serious concerns about freshwater use for oil and gas production regardless of the fact that urban water use and the growth of demand is a much more critical issue.
Grubert, Emily A., Fred C. Beach, and Michael E. Webber. 2012. Can switching fuels save water? A life cycle quantification of freshwater consumption for Texas coal- and natural gas-fired electricity. Environmental Research Letters 7.4 (1 December): 045801.
Life-cycle analysis of water required for electricity generation in Texas by coal plants versus natural gas plants. Includes all stages of advanced hydraulic fracturing for producing shale gas. Conclusion is that the water footprint of thermoelectric generation in Texas would be more than halved by replacing coal with natural gas.
Kondash, A., and A. Vengosh. 2015. Water footprint of hydraulic fracturing. Environmental Science & Technology Letters 2.10: 276–280.
This study builds on previous studies by integrating across several databases (e.g., FracFocus, DrillingInfo, Energy Information Administration, and state and industry sources) to report water usage for the main shale plays in the United States. The use of several sources helps to bridge the naturally fragmented data together into one cohesive paper.
Murray, Kyle E. 2013. State-scale perspective on water use and production associated with oil and gas operations, Oklahoma, U.S. Environmental Science & Technology 47.9: 4918–4925.
Water and oil and gas activities are regulated by states. Water use for oil and gas development in Oklahoma is projected to increase threefold by 2060. Necessary changes include water conservation, reuse of produced water, and use of alternative fracturing fluids such as nitrogen that use less water.
Nicot, Jean-Philippe, and Bridget R. Scanlon. 2012. Water use for shale-gas production in Texas, U.S. Environmental Science & Technology 46.6 (20 March): 3580–3586.
The use of water in shale gas plays in Texas estimated from well completion data. Future demands estimated by extrapolation. Groundwater overdrafts in the future could easily occur. Although the total use of water for hydrofracturing is relatively small, it can have major impacts locally.
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